1. Field of the Invention
The present invention relates to a surface inspection method which measures information on a minute contaminant particle and a defect on a semiconductor substrate (semiconductor wafer), and surface roughness of the substrate.
2. Description of the Related Art
In a production line for semiconductor substrates (semiconductor wafers), inspection for defects such as a contaminant particle attached to the surface of the semiconductor substrate and a scratch generated during processing is performed in order to observe a state where dust is generated in a manufacturing apparatus. For example, in the semiconductor substrate before forming a circuit pattern, a minute contaminant particle and a defect not larger than several 10 nm on the surface thereof need to be detected. Furthermore, a crystal defect existing in a shallow region adjacent to the substrate surface and surface roughness of the substrate surface are also become inspection objects other than the contaminant particle and the defect as the inspection of the surface of the semiconductor substrate.
As for technology for detecting a minute defect on the surface of an object to be inspected such as a semiconductor substrate, for example, as disclosed in U.S. Pat. No. 5,798,829, a focused laser luminous flux is irradiated onto the surface of the semiconductor substrate; scattered light generated in the case where a contaminant particle is attached to the semiconductor substrate is detected; and a contaminant particle and a defect on the entire surface of the semiconductor substrate are inspected by rotation and translation feed of the semiconductor substrate.
It is configured such that an ellipsoidal mirror is used for detecting scattered light, a detection position on the semiconductor substrate is set to a primary focus position of an ellipse, and the light receiving surface of a light receiving element is arranged on a secondary focus position; and accordingly, the scattered light generated at the contaminant particle can be collected with a wide solid angle, and a minute contaminant particle can also be detected.
In the technology disclosed in U.S. Pat. No. 5,798,829, a laser luminous flux which is for illuminating the semiconductor substrate includes both oblique illumination and normal illumination with respect to an elevation angle to the substrate surface; however, only an illumination luminous flux from only one azimuthal angle is provided with respect to one elevation angle.
In addition, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-255278, there is provided one in which a condenser lens and a photodetector are arranged at a position where a plurality of elevation angles and a plurality of azimuthal angles are combined with respect to the surface of a semiconductor substrate, and scattered light focused by each condenser lens is detected by the photodetector; and accordingly, detection in an advantageous direction can be enabled in accordance with three-dimensional irradiation distribution characteristics of the scattered light from a minute contaminant particle.
Also in the technology disclosed in Japanese Patent Application Laid-Open No. 2001-255278, a laser luminous flux which is for illuminating the semiconductor substrate includes two oblique illumination and normal illumination; however, only one azimuthal angle of the laser luminous flux corresponding to one incident angle (elevation angle) is provided.
Furthermore, in Japanese Patent Application Laid-Open No. 2001-235431, technology which uses two laser light sources having different wavelengths for a light source; and in this technology, illumination light from two laser light sources are incident to the surface of the semiconductor substrate from the same azimuthal angles but with different incident angles, that is, with different elevation angles.
In addition, in the technology disclosed in Japanese Patent Application Laid-Open No. 11-223607, technology in which the surface of the semiconductor substrate is illuminated at different two azimuthal angles from substantially the same elevation angles using two laser light sources having different wavelengths; however, the two azimuthal angles in this case have mutually different directions by 180°, and two illumination regions have a relation in parallel with each other.
In the above prior art, if illumination is performed from one azimuthal angle, as generally shown in FIG. 15, an illumination beam 21 is incident to an irradiation region on the semiconductor wafer along a direction of a straight line which connects the illumination region to the rotational center of rotation operation that is primary scan of a movement stage for an object to be inspected. In this case, as shown in FIG. 16, an (x, y) coordinate system fixed on the surface of the semiconductor wafer having a cutout portion 300 whose crystal orientation can be identified, is taken.
When the semiconductor wafer is rotationally moved and illuminated by the illumination beam 21 from a fixed direction, a point A on the semiconductor wafer is illuminated from a direction in parallel with a y-axis of the (x, y) coordinate system; however, a point B is illuminated from a direction in parallel with an x-axis. In addition, a point C is illuminated from a direction making 45° with the x-axis and the y-axis, which is at a position intermediate therebetween.
In the case where a contaminant particle and a defect having such an anisotropy that depends on an incidence direction of the illumination light are attached to the surface of the semiconductor wafer, intensity of the scattered light generated by the illumination light differs according to which position on the semiconductor wafer the contaminant particle or the like is attached to. Therefore, it is to be expected that there generates a difference in detection sensitivity and there arises an error when the size of the contaminant particle and the defect are calculated on the basis of the scattered light intensity.
In addition, in a semiconductor wafer polished to extremely enhance flatness of the surface, there appears surface roughness having a level close to an atomic arrangement step which constitutes the surface thereof; however, and such arrangement step generally appears having a large correlation with crystal orientation of the semiconductor wafer. Therefore, if the same position of such semiconductor wafer is illuminated from the same elevation angle with different azimuthal angle; scattered light having different intensity is generated.
That is, if such semiconductor wafer is illuminated by illumination light from different directions by the rotational movement, even in the case where the entire surface of the semiconductor wafer has uniform surface roughness, scattered light which differs in its intensity for each rotation angle with the primary scan rotation of the movement stage for the object to be inspected is observed. This often occurs in an actual surface inspection apparatus, and intensity distribution on the semiconductor wafer of a signal derived from the surface roughness of the semiconductor wafer (referred to as “haze signal” below) often becomes as shown in FIG. 17, for example.
FIG. 17 shows that the haze signal is large in the order of a→b→c→d→e→f→g. The anisotropy of detection sensitivity of the haze signal has an influence on also the detection sensitivity of the contaminant particle and the defect. That is, it is well known that a noise level at the time of detecting the scattered light from the contaminant particle and the defect depends on fluctuation (shot noise) of the scattered light derived from the surface roughness, and a threshold at the time of detecting a signal from the contaminant particle and the defect needs to be increased at a portion where the haze signal is high; and as a result, the detection sensitivity of the contaminant particle and the defect decreases.